The invention relates to a rock drill for a hammer drilling machine. The rock drill comprises one of a single thread and a multi-thread discharge helix. A drill head is connected with the discharge helix and has an end face, and a cross-section taken approximately transverse to a longitudinal axis of the drill. The cross-section is defined by two mutually opposite, approximately axially parallel side flanks which form respective drilling dust grooves. A main cutting tip is arranged on the end face and extends over an entire diameter of the drill head to project radially beyond an outer circumferential contour thereof. The main cutting tip is comprised of a hard metal, and is inclined in a shape of a-roof as viewed relative to side thereof. Further, the main cutting tip includes two cutting edges. An auxiliary cutting tip is arranged transversely to the main cutting tip.
Rock drills having hard metal cutting tips are used for making holes in concrete, masonry, rock or the like. The drill head is in this case provided on its end face with at least one hard metal cutting tip, which generally extends over the entire diameter of the drill head and which through the rotary percussion or rotary hammering drive of the drill exerts a chisel action on the stone material which is to be comminuted. The diameter of the drilled hole is dictated by the outside diameter of the hard metal cutting tip. Such tools have the disadvantage that the cutting edges of only one cutting tip are subjected in the outer region to considerable wear through the heavy stressing, so that drilling progress soon declines.
In order to reduce the surface pressure on a single hard metal cutting tip and thus to lengthen the cutting edge life of the drill head, so-called cross cutting elements have become known, in which two auxiliary cutting tips are arranged at right angles to a main cutting tip (DE-A1 29 12 394). In this known tool the drill head has an approximately rectangular shape in cross section, with an inherently circular basic cross section with lateral flats to form spacious drilling dust grooves. These cross cutting elements are inserted symmetrically and centrally in the approximately rectangular cross section, that is to say the main cutting tip extends centrally and parallel to the two drilling dust clearance grooves. Such an arrangement of a drill head having a main cutting tip arranged parallel to the side surfaces of the drilling dust grooves, and also having auxiliary cutting tips disposed at right angles thereto, has the disadvantage that, because of the rectangular cross-sectional shape of the drill head, the auxiliary cutting tips in particular have only a very short length so as to not project too far into the drilling dust groove space. Consequently, the auxiliary cutting tips, whose operative diameter is shorter, cannot support the main cutting tip in the diameter region in which the diameter of the main cutting tip projects beyond the diameter of the auxiliary cutting tip. It is, however, precisely the regions of the main cutting tip which lie radially on the outside diameter that need support by the auxiliary cutting tips in order to improve the material removal work.
From EP 0 281 997 B1 or from EP 0 322 565 B1 rock drills have become known, which have a substantially square drill head cross section. The main cutting tip and two auxiliary cutting tips at right angles thereto connect the respective corner points of the square cross section. This arrangement has the advantage over the subject of the previously mentioned publication that the main and auxiliary cutting tips have approximately the same outside diameter, so that the auxiliary cutting tips form an effective support for the main cutting tip even in the radially outer region. Where the cross section in one exemplary embodiment of these known drilling tools changes from the square cross section and leads to a rectangular cross section, the subject of these known publications still retains an arrangement of the main cutting tip and the auxiliary cutting tips at right angles to one another. The auxiliary cutting tips in particular consequently lead into the side region of the drilling dust grooves and are possibly not given optimum support by the drill head.